Characterization of Groundwater Samples from Superfund Sites by

Nov 27, 1996 - Groundwater at or near Superfund sites often contains much organic matter, as indicated by total organic carbon (TOC) measurements. Ana...
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Environ. Sci. Technol. 1996, 30, 3558-3564

Characterization of Groundwater Samples from Superfund Sites by Gas Chromatography/Mass Spectrometry and Liquid Chromatography/Mass Spectrometry LEON D. BETOWSKI* U.S. Environmental Protection Agency, National Exposure Research LaboratorysCharacterization Research Division, P.O. Box 93478, Las Vegas, Nevada 89193-3478

DOUGLAS S. KENDALL U.S. Environmental Protection Agency, Office of Enforcement, National Enforcement Investigations Center, P.O. Box 25227, Denver, Colorado 80225

CHRISTOPHER M. PACE AND JOSEPH R. DONNELLY Lockheed Martin Environmental Services Group, 980 Kelly Johnson Drive, Las Vegas, Nevada 89119

Groundwater at or near Superfund sites often contains much organic matter, as indicated by total organic carbon (TOC) measurements. Analyses by standard GC and GC/MS methodology often miss the more polar or nonvolatile of these organic compounds. The identification of the highly polar or ionic compounds may be needed to assess toxicity more reliably, to plan remediation, and to establish the possible source of a waste and the responsible party. This study characterized water samples from two Superfund sites for organic components where routine methods had failed to account for a majority of the TOC. Carboxylic acids, alcohols, and ketones were detected by GC/MS using a new capillary column designed for polar organic compounds. Particle beam LC/MS allowed for identifying several additional compounds. Finally, thermospray LC/MS was shown to be an excellent means of detecting ionic constituents, such as aromatic sulfonic acids, in the water samples.

Introduction The organic content of groundwater at or near Superfund sites is often high, as indicated by total organic carbon (TOC) measurements (1). However, standard analyses based on gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) are focused on target compounds and often identify and quantify only a small * Corresponding author telephone: (702)798-2116; fax: (702)7982142; e-mail address: [email protected].

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percentage of the organic content (2) as measured by the TOC method. The identification of the highly polar or ionic compounds is needed to more reliably assess toxicity (2), to plan remediation, and to establish the possible source of a waste and the responsible party. The purpose of this study, undertaken by the National Exposure Research Laboratory, Characterization Research Division, of the U.S. Environmental Protection Agency, was to characterize the groundwater samples from two Superfund sites more fully for organic components. Prior, routine GC-based methods of organic analysis failed to account for most of the TOC. Therefore, analyses of the samples by particle beam liquid chromatography/mass spectrometry (PB LC/MS) and thermospray (TSP) LC/MS were performed, in addition to GC/MS. These LC/MS techniques improve the identification and analysis of the unknown polar organic compounds. In addition, Beihoffer and Ferguson (3) used a GC column coated with an acidified polyethylene glycol phase for GC/ MS determination of selected carboxylic acids and alcohols in groundwater from a Superfund site. The use of this column enabled the quantification of acids and alcohols that composed nearly 50% of the TOC. Previous analysis using routine GC/MS methods had accounted for less than 1% of the TOC (3). PB LC/MS produces electron impact (EI) ionization type mass spectra, which can provide a substantial amount of structural information for identification purposes (4), and are amenable to computerized library searches using standard EI spectra. In recent reports on characterizing the Stringfellow Superfund site in California, PB anionexchange LC/MS and LC/UV analysis showed that more than 95% of the TOC comprised chlorinated aromatic sulfonic acids, with 4-chlorobenzene sulfonic acid comprising up to 69% of the TOC (5-7). This technique was used to determine six other aromatic sulfonic acids in aqueous environmental samples (8, 9). However, PB LC/MS is not a universal technique for all intractable compounds. Analyte carryover has been reported (8, 9). Thermal decomposition contributions to the mass spectra of chlorinated phenoxy acid herbicides were found (10) as were enhanced ion abundances due to a “carrier effect” (11). A complementary technique to PB LC/MS is TSP LC/ MS, a “soft” ionization technique that produces molecular weight information for a wide variety of organic compounds (12). Unlike PB, thermospray does not rely on external ionization. The two major processes that produce ions in thermospray are ion evaporation and chemical ionization. In the PB interface, the molecule volatilizes on a hot surface and ionizes by electron bombardment or chemical ionization. The thermospray process is more amenable to ionic and thermally labile compounds than PB. In a work related to the present study, TSP LC/MS was used to confirm that approximately half of the unidentified total organic halocarbon (TOX) content in leachates from the BKK hazardous waste site in Southern California is 4-chlorobenzene sulfonic acid. Only 4% of the TOX had been previously identified using standard GC-based methods (13).

S0013-936X(96)00220-9 CCC: $12.00

 1996 American Chemical Society

The characterization of groundwater presupposes an efficient extraction of organic compounds from an aqueous medium. Bruchet et al. discussed the potential of several extraction and MS detection techniques for the characterization of natural and drinking waters (14). GC/MS/MS was used as the analysis technique whenever possible, with the nonvolatile and thermally labile compounds being analyzed by high-temperature GC, capillary-column supercritical fluid chromatography, pyrolysis GC/MS, TSP LC/ MS/MS, and FAB MS/MS. The use of this multi-technique approach provided more knowledge of the organic carbon constituents in water, taking into account widely different volatilities, polarities, and thermal stabilities. In this study, we adopt a similar strategy in using a variety of techniques to characterize Superfund groundwater samples. A combination of GC/MS, PB LC/MS, and TSP LC/MS was used to identify compounds extracted by several methods. The carbon accounted for by these analyses was compared with the TOC measurements.

Experimental Section Reagents. Propanoic, 2-methylpropanoic, butanoic, pentanoic, hexanoic, and heptanoic acids were obtained from the THETA Corp. (Newton Square, PA). Phthalic acid, benzoic acid, p-chlorobenzenesulfonic acid, xylenesulfonic acid sodium salt, dodecyl sulfate sodium salt, and p-dodecyl benzenesulfonic acid sodium salt were obtained from Aldrich (Milwaukee, WI). Instrumentation. GC/MS analyses were performed using a Hewlett-Packard (HP) 5988A GC/MS system. The mass spectrometer was operated in the electron impact ionization mode with an ionizing energy of 70 eV and an emission current of 300 µA. The ion source temperature was 200 °C. The mass spectrometer was scanned from 35 to 350 Da at a rate of about 1 scan/s. Methylene chloride extracts were analyzed primarily using a J&W Scientific (Folsom, CA) 30 m × 0.25 mm i.d. DB-FFAP capillary column. The injection port and transfer line were maintained at 250 °C. Helium was used as the carrier gas with a linear flow rate of 40 mL/s. The temperature of the column was initially held at 40 °C for 1 min and then programmed to 250 °C at a rate of 7 °C/min. The instrument was tuned with perfluorotributylamine using the autotune program provided in the MS software. Liquid chromatographic separations used a 25 cm × 2.1 mm i.d. Supelco LC-18-DB column with 5-µm particle size and a flow rate of 0.2 mL/min. The solvent program consisted of 4 min with 100% 0.02 M aqueous ammonium acetate, programming to 100% methanol over 36 min, and isocratic with 100% methanol for an additional 5 min (45 min total analysis time). Equilibration of the column was accomplished employing the initial conditions for 10 min prior to the next injection. The PB LC/MS system consisted of a HP 1090L LC, HP 59980A PB interface, and an HP 5988A quadrupole MS. The PB interface was operated with a desolvation chamber temperature of 45 °C. The nebulizer capillary position and helium flow rate were set to maximize response to the m/z 184 ion from a 1-µL injection of 10 ng/µL benzidine under flow injection and selected ion monitoring (SIM) conditions. The MS was operated in the EI mode with an ion source temperature of 280 °C, 70 eV electron energy, and 300 µA emission current. The instrument was tuned with perfluorotributylamine to maximize the m/z 414 ion. The mass spectrometer was scanned from 65 to 500 Da at a rate of

0.4 scans/s. Computerized library (15) searches were performed to identify compounds by their EI and PB mass spectra. The TSP LC/MS system consisted of a HP 1090L LC, ISCO LC-5000 precision syringe pump (Lincoln, NE), HP TSP interface, and an HP 5988A quadrupole MS. Negativeion and positive-ion TSP analyses used the filament-on mode with a 276 °C ion source temperature. The mass spectrometer was scanned from 120 to 500 Da in negativeion mode and from 122 to 500 Da in positive-ion mode. For SIM data acquisition, a dwell time of 500 ms for each ion was used, resulting in 0.3 cycles/s. Aqueous ammonium acetate (0.1 M) was added post-column using the precision syringe pump at a rate of 1.0 mL/min. The TSP ion source was tuned with polypropylene glycol. The TSP stem temperature was adjusted to provide 95-100% vaporization, as determined by the probe survey scans. Sample Extraction. For GC/MS analysis, 100 mL of each groundwater sample was acidified (pH < 2) and extracted four times with 40 mL of methylene chloride in a separatory funnel. The extracts were concentrated to 1 mL for analysis. For LC/MS analysis, an aliquot of each sample was taken to dryness using a rotary evaporator at 40 °C under reduced pressure. The samples were then reconstituted in methanol. Inorganic salts were removed by filtration followed by the addition of acetone (1:1), refiltration, evaporation to dryness under a stream of nitrogen, and reconstitution to the desired volume in methanol. Alternatively, the samples for LC/MS analysis were lyophilized with a Virtis Sentry (5-L) unit instead of using the rotary evaporator. Direct aqueous injections of non-extracted groundwater samples were also used for LC/MS analysis. Total Organic Carbon. TOC measurements followed procedures described in EPA Method 415.2 (16) and SW846 Method 9060 (17).

Results Groundwater samples from two Superfund sites were analyzed by GC/MS, PB LC/MS, and TSP LC/MS to characterize the organic content beyond that possible by routine GC-based methods. The results for site A (samples A1 and A2) and site B (samples B1 and B2) are discussed below. Gas Chromatography/Mass Spectrometry. Initial GC/ MS analysis of the methylene chloride groundwater extracts used a poly(5% diphenyl/95% dimethylsiloxane) bondedphase column (J&W DB-5), the standard column type for the analysis of semivolatile organic compounds. This column provided poor peak shape; large fronting peaks were found with each of the groundwater samples analyzed (e.g., sample A2, Figure 1a). This type of poor chromatography is often problematic for automated data system identification and quantification of unknown compounds. These peaks may be missed by computer search routines, and broad peaks are more likely to coelute with other compounds, providing combined mass spectra that are difficult to interpret and to use for quantification. Analyses of the extracts were then performed using a nitroterephthalic acid-modified polyethylene glycol phase column (J&W DB-FFAP). This column is specifically designed for analysis of acidic compounds such as fatty acids and phenols. Figure 1b displays the GC/MS TIC of an extract of sample A2 using the DB-FFAP column, displaying improved resolution and peak shape compared to the chromatogram in Figure 1a. Similar improvements

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TABLE 1

Extraction Results for Nine Carboxylic Acids and Phenol compound

av % recovery 1 mg/L (n ) 3)

recovery % RSD (n ) 3)

% recovery matrix spike sample B2

acetic acid propanoic acid 2-methylpropanoic acid butanoic acid 3-methylbutanoic acid pentanoic acid hexanoic acid heptanoic acid benzoic acid phenol

2 (10 mg/L) 13 41 44 74 80 84 92 84 71

0.082 2.1 1.6 0.95 3.3 6.3 4.6 6.8 0.60 7.0

2 12 35 40 75 70 84 93 75 66

TABLE 2

Estimated Concentrations (in mg/L TOC) for Sample Constituents from Superfund Sites A and B concn (mg/L) of organic carbon

FIGURE 1. GC/MS TIC of a methylene chloride extract from sample A2 using the (a) DB-5 and (b) DB-FFAP GC columns.

in signal to noise ratios and hence detection limits were obtained for a mixture of seven organic acid standards with the DB-FFAP column. For quantification, a three-point calibration curve was constructed for each of the eight carboxylic acids and phenol, using the DB-FFAP column over a concentration range of 25-400 ng/µL. Response factors were determined using the integrated peak areas of the base ions in each mass spectrum. Other tentatively identified compounds in the groundwater samples were quantified using integrated TIC peak area for each compound versus that of the internal standard (d5-phenol). Methylene chloride extraction efficiency of nine watersoluble low molecular weight carboxylic acids and phenol were investigated in blank water and in sample B2 (see Table 1). Recoveries for the four smallest carboxylic acids were poor but reproducible. Quantitative results were corrected for recoveries only for cases where recoveries had been determined. Other results assume 100% recovery. Up to 84 major chromatographic peaks were observed in the methylene chloride sample extracts from the two sites, with an average of 80% tentatively identified by computer library searches. The majority of the compounds in all four samples were carboxylic acids, alcohols, ketones, or alkylbenzenes. Samples from site A also contained a series of chlorinated pyridines. Table 2 lists some of the compounds that made relatively large contributions to the TOC at sites A and B. Liquid Chromatography. The LC conditions used volatile mobile phase components (acids, bases, and

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compound

A1

A2

B1

acetic acid benzoic acid 1-butanol 2-butanol butanoic acid 2-butanone 2-butoxyethanol cyclohexanecarboxylic acid cyclohexanol cyclohexanone heptanoic acid hexanoic acid 3-methylbutanoic acid methylene chloride 2-methylhexanoic acid 2-methylpentanoic acid 2-methylpropanoic acid 3-methylpropanoic acid pentanoic acid phenol phenylacetic acid phenylbutanoic acid propanoic acid tetrahydrofuran

948

664

65 2.5

126 64 63 814 184

40 77 118 185

% TOC accounted for

B2 25

2.3 3.4

3.9

109 153 1.3 5.6 3.5 81

54 4.1 1.9 2.5 4.2

5.5 4.3

154

64 3.5 51

78

48 45

3.3 1.0 15

33

43

85

49

buffers) for PB and TSP LC/MS compatibility. Reverse phases contained methanol or acetonitrile with aqueous medium ammonium acetate, ammonium formate, acetic acid, formic acid, or ammonium hydroxide at pH between 2 and 8. Gradient elution with ammonium acetate/ methanol provided the best separation and peak shape. Figure 2 displays the LC chromatogram (UV detection at 230 nm) from a 25-µL injection of filtered water sample B1. The peak shapes of early eluting components were not improved by acidic or basic conditions. These components may be highly polar or ionic in nature. The chromatogram of sample B2 was very similar to that of B1. Likewise, samples A1 and A2 were similar in appearance to each other. Particle Beam LC/MS. Table 3 lists the compounds observed in samples from sites A and B by PB LC/MS analysis that were tentatively identified through a library search. The PB LC/MS TIC from sample B1 displayed multiple peaks superimposed on a large chemical noise “hump” eluting from ca. 15 to 35 min; mass spectra and

FIGURE 2. LC chromatogram (230 nm) from a 25-µL injection of sample B1 (filtered). TABLE 3

Tentatively Identified Compounds Using PB LC/MS in Superfund Groundwater Samples site A

RT (min) 3.0

site B compound

oxotetramagnesium pentacetate

16.2

3-(2-hydroxypropyl)-5-methyl-2-oxazolidinone

20.0

xylenesulfonic acid

21.5 23.3

phenol 4-toluenesulfamide

25.1

(2,4-dichlorophenoxy)acetic acid

28.1

2-(2,4-dichlorophenoxy)propanoic acid

identifications of four components are presented in Figure 3. Such high background levels are seen when high concentrations of poorly volatile organics, such as acids or acid herbicides, are present in the ion source (10). Thermospray LC/MS. Molecular weight information for many organic compound classes can be obtained using TSP. For positive-ion detection, samples must be more basic than the mobile phase to form (M + H)+ ions or be sufficiently polar to form stable adduct ions such as (M + NH4)+. For negative-ion detection, samples must be more acidic than the mobile phase to form (M - H)- ions. In

RT (min)

compound

3.0 11.7 13.8

oxotetramagnesium pentacetate benzoic acid phenylacetic acid

19.7 20.0 20.9

phenylpropanoic acid xylenesulfonic acid naphthalenecarboxylic acid

23.3 23.7 24.2 24.4

4-toluenesulfamide S-benzenethiopropanoic acid phenylbutanoic acid naphthalenecarboxylic acid

26.6 27.5 29.0 29.8 30.8 33.9

1(2H)-isoquinolinone S-benzylthiopropanoic acid 2(3H)-benzothiazolone N-ethyl-4-methylbenzenesulfamide phenylhexanoic acid 4,4′-isopropylidenediphenol

general, the positive-ion mode is more sensitive for basic compounds, while the negative-ion mode is better for acidic analytes. TSP full-scan analysis of the concentrated water samples, using both positive and negative ionization, detected many components. Tentative identifications were limited to those compounds for which standards were available (two aromatic carboxylic and five sulfonic acids) and those found by PB LC/MS (Table 3). Negative-ion TSP was much more sensitive for the detection of acidic compounds than positive ion.

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TABLE 4

TSP LC/MS Retention Time, Selected Ions, and Instrument Detection Limits for Carboxylic and Sulfonic Acids Standards RT (min) 3.3 10.8 21.8 24.8 29.8 46.5 47.0

compound phthalic benzoic p-chlorobenzenesulfonic xylenesulfonic acid sodium salt p-cumenesulfonic acid sodium salt dodecyl sulfate sodium salt dodecyl benzenesulfonic acid sodium salt

Figure 4 displays the negative-ion full-scan (120-500 Da) TSP LC/MS TIC of the concentrated sample B1. Isotopic clusters containing several Br or Cl atoms or both were observed at masses up to about 500 Da. Example negativeion TSP mass spectra are shown in Figure 5 for the four labeled peaks in Figure 4. A component tentatively identified as phenylacetic acid (Figure 5a) shows the typically high intensity (M + OAc)- and (M - H)- ions. The (2M - H)- ion usually has lower relative intensity. In contrast, Figure 5b, tentatively identified as a xylenesulfonic acid isomer, has a base peak of (M - H)- ion at m/z 185 (m/z 285 is due to a coeluting compound), while (M + OAc)- is not observed. These typical spectral features can be used to differentiate between these two classes of compounds more reliably than the 32S:34S isotopic abundance ratio, because coeluting compounds in environmental samples may cause interferences to the isotopic ratio measurement. A mixture of two carboxylic acids and five sulfonic acids was used for quantification with negative-ion single-ion monitoring (SIM) TSP. Table 4 lists the standards and retention times, SIM ion, and estimated instrument detection limits. Average response factors were calculated using the integrated peak areas of the molecular anions taken at two concentrations differing by a factor of 10. Direct aqueous injection of the water samples with TSP negative-ion SIM LC/MS was performed with dilution as needed (samples A1 and A2) to prevent coprecipitation of the xylenesulfonic acid with inorganic salts. Standards were used to estimate quantities in samples A1, A2, B1, and B2, respectively, as 40, 36, 3, and 1 mg/L benzoic acid and 202, 87, 2, and 6 mg/L xylenesulfonic acid. Total Organic Carbon. The TOC measurements in the four Superfund groundwater samples A1, A2, B1, and B2 were 7980, 3370, 165, and 139 mg/L, respectively. Of these amounts, the organic acids accounted for 15%, 29%, 86%, and 54%, respectively. Percentages due to conventional volatile vs semivolatile organics were approximately evenly divided in each sample; their summed percentages were 28%, 24%, 5%, and 2%, respectively, in the four samples. These analyses were performed by GC/MS using the DBFFAP column, except for the volatiles, which were determined by purge and trap GC/MS, and xylenesulfonic acid, which was measured by negative-ion TSP-LC/MS. These results and those shown in Table 2 indicated that much of the TOC content was highly water-soluble organic compounds such as carboxylic acids, ketones, and alcohols. The use of a specialized GC column allowed for increased resolution for many compounds and successful chromatography of the carboxylic acids. The current methods for volatiles and semivolatiles that are used in programs such as the Contract Laboratory Program, which supports

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SIM ion

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H)-

165 (M 181 (M + OAc)191 (M - H)185 (M - Na)199 (M - Na)265 (M - Na)325 (M - Na)-

IDL (ng) 4 0.5 5 3 7 1 4

FIGURE 3. Electron impact PB LC/MS mass spectra of four compounds tentatively identified in the concentrated B1 water sample: (a) phenylacetic acid, (b) xylenesulfonic acid, (c) naphthalenecarboxylic acid, (d) N-ethyl-4-methylbenzenesulfonamide.

evaluation of Superfund sites, may miss these highly polar compounds and may profit from use of these columns. PB LC/MS was capable of identifying components (Table 3) in addition to those identified by GC and GC/MS methods. The problems of the particle beam interface are well documented (see ref 9, for example). Analytes subject to thermal degradation will show anomalous behavior on introduction into the PB interface, and volatile compounds tend to be purged with the solvent by the momentum separator of the interface. However, PB LC/MS remains a valuable technique for many classes of compounds that are not amenable to GC methods. TSP LC/MS proved to be a sensitive technique in this study for aromatic carboxylic acids and sulfonic acids, when

FIGURE 4. Negative ion TSP LC/MS TIC of a concentrated B1 water sample.

operated in negative-ion mode. Since thermospray is a soft ionization technique, few characteristic ions are produced in the spectrum of any one compound. Therefore, unknowns are difficult to identify without ancillary techniques such are MS/MS, which was not available for the present study. The commercial availability of economical ion trap mass spectrometers capable of MS/MS modes of detection and LC introduction suggests that future methods will use this technology for identification of unknowns. In one of the four groundwater samples examined in this study, the tentatively identified compounds accounted for almost all of the entire TOC measured. For the other three samples, compounds were tentatively identified that accounted for approximately 50% of the carbon concentration. Problems responsible for incomplete characterization of these samples included compounds not being extracted or being lost in the extraction process, wrong assumptions of extraction efficiency, and lack of standards for identification (especially in thermospray introduction). These groundwater samples contained high concentrations of inorganic salts. In the precipitation and removal of these inorganic salts, organic salts were also subject to losses. Many of the compounds that were identified and quantified were assumed to be extracted at 100% efficiency, unless an extraction study was performed on the analyte. As shown in this study, lower extraction efficiencies are probably to be expected. Finally, many of the peaks in the chromatogram from the thermospray LC/MS of these samples were not identified nor quantified due to lack of standards. FIGURE 5. Negative ion TSP LC/MS mass spectra of four compounds tentatively identified in the concentrated B1 water sample: (a) phenylacetic acid, (b) xylenesulfonic acid, (c) naphthylenecarboxylic acid, (d) S-benzylthiopropanoic acid.

This work indicates that a major fraction of compounds is not detected by routine environmental analysis. The LC/MS techniques and specialized GC columns are valuable additions to the routine volatile and semivolatile GC/MS technologies for groundwater samples. Even with these

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advanced techniques, up to or more than 50% of the TOC measurement may still be unidentified in certain samples. Future efforts to characterize unknowns in environmental samples may include better extraction or concentration techniques for water-soluble organic compounds and the separation techniques of micro-bore LC, capillary LC, and capillary electrophoresis combined with electrospray MS and ion trap MS/MS.

Acknowledgments The U.S. Environmental Protection Agency (EPA), through its Office of Research and Development (ORD), funded and performed the research described here. It has been subjected to the Agency’s peer review and has been approved as an EPA publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

Literature Cited (1) Bramlett, J.; Furman, C.; Johnson, A.; Ellis, W. D.; Nelson, H.; Vick, W. H. EPA project summary. EPA/600/S2-87/043; Environmental Protection Agency: Washington, DC, 1987. (2) Coleman, W. E.; Munch, J. W.; Kaylor, W. H.; Streicher, R. P.; Ringhand, H. P.; Meier, J. R. Environ. Sci. Technol. 1984, 18, 674-681. (3) Beihoffer, J.; Ferguson, C. J. Chromatogr. Sci. 1994, 32, 102-106. (4) Willoughby, R. C.; Browner, R. F. Anal. Chem. 1984, 6, 26262631. (5) Kendall, D. S. Anal. Chim. Acta 1989, 219, 165-169.

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(6) Brown, M. A.; Kim, I. S.; Roehl, R.; Sasinos, F. I.; Stephens, R. D. Chemosphere 1989, 19, 1921-27. (7) Kim, I. S.; Sasinos, F. I.; Stephens, R. D.; Brown, M. A. Environ. Sci. Technol. 1990, 24, 1832-1836. (8) Kim, I. S.; Sasinos, F. I.; Dharmendra, K. R.; Stephens, R. D.; Brown, M. A. J. Chromatogr. 1991, 589, 177-183. (9) Hsu, J. Anal. Chem. 1992, 64, 434-443. (10) Betowski, L. D.; Pace, C. M.; Roby, M. R. J. Am. Soc. Mass Spectrom. 1992, 3, 823-830. (11) Bellar, T. A.; Behymer, T. D.; Budde, W. L. J. Am. Soc. Mass Spectrom. 1990, 1, 92-98. (12) Yergy, A. L.; Edmonds, C. G.; Lewis, I. A. S.; Vestal, M. L. Liquid Chromatography/Mass Spectrometry; Plenum Press: New York and London, 1990; Chapter 4. (13) Stephens, R. D.; Ball, N. B.; Fisher, T. S.; Roehl, R.; Draper, W. M. Proceedings of the U.S. EPA Symposium of Waste Testing and Quality Assurance; U.S. Government Printing Office: Washington, DC, 1987; Vol. 1, p 15. (14) Bruchet, A.; Legrand, M. F.; Arpino, P.; Dilettato, D. J. Chromatogr. 1991, 562, 469-480. (15) McLafferty, F. W.; Stauffer, D. B. Wiley/NBS Registry of Mass Spectral Data; Wiley: New York, 1989. (16) Methods for Chemical Analysis of Water and Wastes; EPA 600/ 4-79-020; U.S. EPA: Cincinnati, OH, 1983. (17) Test Methods for Evaluating Solid Waste; Office of Solid Waste and Emergency Response, U.S. Environmental Protection Agency: Washington, D.C., 1986.

Received for review March 8, 1996. Revised manuscript received July 26, 1996. Accepted July 31, 1996.X ES9602206 X

Abstract published in Advance ACS Abstracts, October 15, 1996.